Complement System in Experimental Autoimmune Anterior Uveitis

Abstract

Abstract: : Purpose: To explore the role of the complement system in experimental autoimmune anterior uveitis (EAAU). Methods: The role of the complement system in EAAU was explored by using cobra venom factor (CVF). EAAU was induced in two panels of Lewis rats (n=12/group) by immunization with bovine melanin associated antigen (MAA). In the experimental panel complement was depleted by a single injection of CVF (160 µg/rat, i.p.) given at day 9 post–immunization. Serum complement levels were monitored using CH50 hemolytic assay. Controls were injected with an equal amount of normal saline. Clinical and histopathological examination was used to determine the onset and severity of disease. Lewis rats (n=6/time point) were also sacrificed at day 10, 12, 14, 16 and 19 post–immunization. Eyes and popliteal lymph nodes were harvested at these time points for RT–PCR analysis for TNF–α, IFN–γ and IL–10. Results: CVF treatment caused almost complete decomplementation, which lasted for 5 days in Lewis rats. CH50 at each time point was less than 5% of the control value. The incidence of EAAU, the duration of the illness and severity of the disease (both clinical and histologic) were dramatically reduced in complement deficient (CVF treated) animals compared to controls (complement sufficient). Using RT–PCR we detected low levels of IFN–γ transcripts in the eyes at day 10 in complement sufficient mice. IFN–γ transcripts within the eye increased at day 12, peaked at day 16 and remained at this maximal levels at day 19 in the presence of complement. Interestingly, IFN–γ mRNA levels did not change and remained at low levels at all five time points in complement depleted rats. Complement depletion resulted in slightly decreased IL–10 mRNA levels at each time point within the eye and no difference in TNF–α mRNA levels was observed in the eyes of complement sufficient and complement deficient rats. Similar mRNA levels for TNF–α, IFN–γ and IL–10 were observed in the popliteal lymph nodes of complement sufficient and complement deficient rats. Conclusions: Our results provide strong evidence that complement activation contributes to the development of EAAU. We also found that the presence of complement is critical for local IFN–γ production during EAAU, which appears to be the major cytokine invovled in the pathogenesis of this disease.

Keywords: autoimmune disease • uveitis–clinical/animal model • cytokines/chemokines